Person $A$ has information partition $\{\{1,2\},\{3,4\},\{5,6\}\}$
Person $B$ has information partition $\{\{1\},\{2,3\},\{4,5\},\{6\}\}$
$w=3$ has been realized.
I'm confused about what $A$ knows that $B$ knows.
At first I thought of it as $K_aK_b(3)=K_a(\{2,3\})=\{1,2,3,4\}$, but the example I found online says $K_aK_b(3)=\{2,3,4,5\}$. why?